Fascinating! whoa!
The only thing that I'd like to mention is Norm's comment to Jake about doing the videolog.
'It'll help keep you sane for the next six years.'
so.. if that's an indication then the next ship won't arrive for 6 years?
I think you're on target with your calculations, but given that quote, maybe every other one only bring supplies but the 6 year one is when people ship out if need be.
But then again... Quaritch told Jake he was getting his legs back and 'out on a shuttle tonight'.
So...he's been there less than a year... which means he would be shipped out on the Venture Star on it's trip back.

Not trying to shoot you down, just trying to piece together the continuity with your math..which is very cool and very worked out. Great stuff!